The use of 3-isothiazolones to control microbial growth in a variety of industrial environments (metal working fluids, cooling tower water, emulsions, plastic film, and the like) has been enhanced by the addition of stabilizers to maintain antimicrobial activity for longer periods of time; typical stabilizer systems include metal nitrates and the like.
U.S. Pat. Nos. 3,870,795 and 4,067,878 teach the stabilization of isothiazolones against chemical decomposition by addition of a metal nitrite or metal nitrate salts, but teach that other common metal salts, including carbonates, sulfates, chlorates, perchlorates, and chlorides are not as effective as nitrates or nitrites in stabilizing solutions of isothiazolones, such solutions usually being in water or in an hydroxylic solvent and immiscible with solvent-soluble isothiazolones.
Formaldehyde or formaldehyde-releasing chemicals are known stabilizers. In certain applications, however, it is desirable to avoid addition of organic stabilizers by virtue of their volatility, decomposition under high heat, higher costs, difficulty in handling, potential toxicity, and the like.
The use of copper as a stabilizer poses two significant problems. Restrictive environmental regulations prohibit the direct discharge of heavy metal salts. This is related to the toxicity of copper ions. These restrictions reduce the use of this biocide (i.e., isothiazolone) in cooling tower applications. Copper also increases the potential for corrosion problems. The use of copper containing biocides must be continually monitored.
The use of ferric chloride to stabilize isothiazolone solutions suffers from a very low pH. This pH range places the product in a hazardous and corrosive category. The presence of iron salts also limits application in paper systems due to concerns regarding brightness reversion of bleached paper.
The present invention eliminates the need for the use of certain metal salts to stabilize the isothiazolone. The potential corrosion problems and known toxicity of some metal salts are thus overcome.